This invention relates generally to mattress foundation structures and more particularly to a box spring assembly of a type which utilizes non-coil springs. Box spring assemblies of this general type have been known since 1964, the first such spring assembly being disclosed in U.S. Pat. No. 3,286,281. Subsequently issued patents disclosing the same general type of box spring assembly are: U.S. Pat. Nos. 3,487,480; 3,506,987; 3,574,240; 3,574,241; 3,665,529; 3,680,157; 3,755,833; 3,824,639; 3,852,838; 4,060,862; 4,120,058; and 4,163,296. Box spring assemblies of the general type shown in the above list of patents, all of which are assigned to the assignee of this application, are advantageous with respect to the conventional box spring assemblies using coil springs because they provide a desired stiffer foundation for the mattress and contain a reduced amount of wire. These box spring assemblies are also advantageous from the standpoints of prolonged service life, ease of assembly and cost of manufacture.
Additional box spring assemblies of this general type are shown in U.S. Pat. Nos. 3,596,299; 3,722,013; 3,825,960; 3,833,948; 3,835,485; 3,869,740; 3,990,121; and 4,000,531.
The present invention provides a formed wire box spring assembly which utilizes improved springs. The spring in the present box spring assembly has an upper portion which yieldably collapses under load to impart a feeling of softness when the bedding occupant first reclines on a mattress supported on the box spring assembly of this invention. This collapse of the upper section is accompanied by a fast build up of resistance to load to reduce the chance of excessive deflection. The initial collapse of the upper section is then followed by a more firm resistance to load by the lower section of the spring which consists principally of a short generally upright length of straight spring wire which functions as a yieldable column supported on still another tension bar to support the bedding load. The column imparts a feeling of firm support to the bedding user following the initial feeling of softness.
The components of the spring end portions are arranged so as to relatively evenly divide the load so that all parts are evenly stressed to avoid any permanent set. The parts are also arranged so as to facilitate the use of stapling tools in securing the springs to the frame.
It is an object of the present invention, therefore, to provide a formed wire box spring assembly having improved formed wire springs capable of imparting a desired feeling of comfort to the bedding user, and which can readily be frame mounted to form the assembly.